Technical Abstract:
In the mid-Atlantic coast region of the United States (39 degrees N latitude, 77 degrees W longitude), the primary strawberry harvest season is from early May to late June. Out-of-season fruit production in the region is low, but the interest for out-of-season strawberry production systems has risen recently. We developed a simple propagation scheme for short-day type strawberry cultivars to produce fruit in fall and spring in high tunnels without using standard conditioning treatments such as chilling or artificial short-day photoperiod, during the nursery phase. Fall flowering occurred in 100 percent of 'Carmine' and 86 percent of 'Camarosa' strawberries, both short-day type cultivars, started as plug plants in early July and maintained in propagation trays until field establishment around 1 September. In 'Carmine' and 'Camarosa' transplants that were started as plug plants in early August, less than 30 percent of transplants produced flowers in the fall. In 2006, July-plugged 'Carmine' and 'Camarosa' strawberry in high tunnel produced an average of 320 and 250 g of marketable fruit from late October to late December. When strawberry plug transplants are grown in tray flats at density of 330 plants m-2 during July and August the leaves form a full canopy with high leaf area index above the plant crowns. The crown near the base of leaf petioles is illuminated only by light in the far-red and near-infrared region. Promotion of flowering in July-plugged transplants is correlated with high ratio of far-red light to visible light reaching the crown. Spectral analyses have shown that no visible radiation less than 700 nm reaches the crown because the shorter wavelength light is absorbed through chlorophyll photosynthesis. The results of this study suggest that transplants of short-day type strawberries that will flower in fall can be produced by developing a plant canopy that alter the light that illuminates the crown. The key physiological mechanism operating in production of short-day type strawberry transplants with high fall flowering potential will be discussed.